Energy-efficient opportunistic scheduling schemes in wireless networks

A key feature in the design of any MAC protocol is the throughput it can provide. In wireless networks, the channel of a user is not fixed but varies randomly. Thus, in order to maximize the throughput of the MAC protocol at any given time, only users with large channel gains should be allowed to transmit. In this paper, a compressive sensing based opportunistic protocol for exploiting multiuser diversity in wireless networks is proposed. This protocol is based on the traditional protocol of R-ALOHA which allows users to compete for channel access before reserving the channel to the best user. We use compressive sensing to find the best user, and show that the proposed protocol requires less time for reservation and so it outperforms other schemes proposed in the literature. Also, as the proposed scheme requires less reservation time, it can be seen as an enhancement for R-ALOHA schemes in fast fading environment.

Cyber-Physical System (CPS) is envisioned to tightly integrate the cyber-world of computation, communication, and control with the physical world. CPS is typically designed as a networked system of interacting sensors, actuators, and embedded computing devices to monitor and control the physical world. Thus, one of the essential building blocks of such a system is a highly efficient networking infrastructure. In this paper, we aims to develop an efficient wireless networking technology which can be utilized in CPS. More specifically, we develop a cross-layer optimization model based on the Network Utility Maximization (NUM) framework and its distributed solution for wireless multihop multicast networks exploiting multi-user diversity. It is known that the capacity of a wireless network can be increased by exploiting different channel conditions at different users, i.e., multi-user diversity; however, it is yet to be determined how much performance gain can be achieved by exploiting multi-user diversity in wireless multihop multicast networks. To address this problem, we extend the NUM framework and derive a new optimization problem including the benefits of multi-user diversity for multicasting scenarios in wireless multihop networks under a probabilistic media access control (MAC). In our problem, multi-user diversity is achieved via opportunistic scheduling. Then, we propose a distributed approximation algorithm for the problem. Our numerical results confirm that the benefit of multi-user diversity is prominent in a wireless multihop network with multicast flows.

This paper proposes a location-based MAC (LMAC) scheme for wireless networks with randomly placed nodes. This scheme regulates channel access by sharing local location information among transmitters. A lattice approximation approach is used to derive upper and lower bound for the success probability for a typical transmission attempt. Numerical results show that with the node density and link distance fixed, the optimal LMAC provides a much higher density of successful transmissions than CSMA and ALOHA.

In this paper, further in-depth asymptotic analysis on the interaction between spatial diversity and multiuser diversity in wireless networks is given, following our recent work [Zhou and Dai, ICC06]. Rigorous proofs and necessarily stronger results in terms of convergence are provided for some intuitions in this area. Equally important, explicit expressions of scheduling gain and average system capacity in various circumstances that reveal interesting inter-connections among key system parameters are given. Our results are general enough to cover many practical scenarios of interesst.

Our contribution, in this paper, is two-fold. First, we analyze the performance of a hierarchical modulation-assisted two-best user opportunistic scheduling (TBS) scheme, which was proposed by the authors, in a fading environment where different users have different average link gains. Specifically, we present a new expression for the spectral efficiency (SE) of the users and using this expression, we compare the degrees of fairness (DOF) of the TBS scheme with that of classical single user opportunistic scheduling schemes, namely, absolute carrier-to-noise ratio (CNR) based single-best user scheduling (SBS) and normalized CNR based proportional fair scheduling (PFS) schemes. The second contribution is that we propose a new hybrid two-user opportunistic scheduling (HTS) scheme based on our earlier proposed TBS scheme. This HTS scheme selects the first user based on the largest absolute CNR value among all the users while the second user is selected based on the ratios of the absolute CNRs to the corresponding average CNRs of the remaining users. The total transmission rate i.e., the constellation size is selected according to the absolute CNR of the first best user. The total transmission rate is then allocated among these selected users by joint consideration of their absolute CNRs and allocated number of information bit(s) are transmitted to them using hierarchical modulations. Numerical results are presented for a fading environment where different users experience independent but non-identical (i.n.d.) channel fading. These selected numerical results show that the proposed HTS scheme can considerably increase the system's fairness without any degradation of the link spectral efficiency (LSE) i.e., the multiuser diversity gain compared to the classical SBS scheme. These results also show that the proposed HTS scheme has a lower fairness in comparison to the PFS scheme which suffers from a considerable degradation in LSE. © 2010 IEEE.

Network protocols in cellular wireless data networks must update routes as a mobile host moves between cells. These routing updates combined with some associated state changes are called handoffs. Most current handoff schemes in wireless networks result in data loss or large variations in packet delivery times. Unfortunately, many applications, such as real-time multimedia applications and reliable transport protocols, adapt to long term estimates of end-to-end delay and loss. Violations and rapid fluctuations of these estimates caused by handoff processing often result in degraded performance. For example, loss during handoff adversely affects TCP performance [4], and high packet loss and variable delays result in poor real-time multimedia performance. In this paper, we describe a multicast-based protocol that eliminates data loss and incurs negligible delays during a handoff. The basic technique of the algorithm is to anticipate a handoff using wireless network information in the form of received signal strengths and to multicast data destined for the mobile host to nearby base stations in advance. This routing, combined with intelligent buffering techniques at the base stations, enables very rapid routing updates and eliminates data loss without the use of explicit data forwarding. We have implemented this protocol using IP Multicast and Mobile IP-like routing. In our implementation, handoffs typically take between 8 and 15 ms to complete and result in no data loss.

The demand for faster internet connections to access wireless multimedia applications, Aeronautical Communication Networks (ACNs) and internet services has resulted into rise of developing broadband wireless technologies in recent years. The demand for higher data rates was the backbone for developing wireless communication technologies such as Worldwide Interoperability for Microwave Access (WiMAX), Long Term Evolution (LTE) and High-Speed Packet Access (HSPA). The big challenge with wireless communications lies with providing Quality of Service (QoS) under various environmental challenges and maximizing resource utilization at the same time. In wireless communication, the support for QoS is difficult due to the unpredictable nature of wireless channels. Opportunistic Scheduling plays a big role towards meeting QoS requirements and managing resources in aeronautical communication networks. Various opportunistic schedulers focus on increasing the system capacity of a wireless communication network, while some aim on improving the system’s fairness and throughput. With such interest in opportunistic scheduling, the paper focuses on reviewing recently proposed opportunistic scheduling algorithms, the objectives they were designed for, and their shortcomings. An effective opportunistic scheduling algorithm with hierarchical modulation technique is presented in this paper. The algorithm focuses on the ability to allocate resources between two users with different channel conditions; that is a user with good channel conditions and a user with bad channel conditions, to maximize the system’s throughput and maintain fairness.

ABSTRACTIn this paper, we study an opportunistic scheduling problem in an OFDMA system, in which sub‐carriers of the system are allocated to each user in each time slot considering the time‐varying channel condition and QoS requirement of each user. We consider two different classes of services that are represented with different types of utility functions. The utility function for a user in one class is defined as a function of its average data rate, which can be applicable to best‐effort services and the utility function for a user in the other class is defined as a function of its instantaneous data rate, which can be applicable to rate‐sensitive services. Those two types of utility functions have been extensively considered in opportunistic scheduling in wireless networks. However, in most of the previous work, they are considered separately in different problems. In this paper, we formulate a stochastic optimization problem that can treat those two types of utility functions in a single problem, which enables us to implement an opportunistic scheduling algorithm that can consider those two classes of services in a single system in a unified way. Through simulations, we first show that our algorithm provides a good approximation to the optimal solution. In addition, we also verify the appropriateness of our utility models. Copyright © 2010 John Wiley & Sons, Ltd.

This paper addresses the Quality of Service (QoS) degradation problem of wireless relay node failures in multihop Worldwide interoperable Microwave Access (WiMAX) and Long Term Evolution (LTE) networks. In general, node protection in a communication network increases the reliability of the traffic flow from source to destination. For wireless networks, implementing the traditional 1+1 protection scheme increases the capital cost, as resources cannot be fully utilized. On the other hand, the design and implementation of the 1:N protection scheme in wireless networks for greater value of N (> 2) is very difficult, due to wireless network coverage and the physical layer design. To overcome the above drawbacks, a technique based on network coding is proposed for node protection in multihop wireless networks. In multihop wireless networks, few research efforts are concentrated on node protection schemes using network coding. Moreover, to best of our knowledge, no reports have been published on measuring the QoS performance for node protection in 4G wireless networks using network coding. In this paper, we first describe the node protection scheme using XOR network coding for multihop 4G wireless networks. Then, we measure the QoS performance, such as packet delivery ratio (PDR), latency and jitter, for different scenarios. The scenarios include a failure of a single relay node and failures of two relay nodes with and without our protection scheme and user's mobility. The simulation results show that the QoS performance with protection against a single relay node failure and failures of two relay nodes are very close to that of no failure scenario, while the network reliability increases due to the protection mechanism. Also, we report a decoding problem in multihop wireless networks using XOR network coding.

This paper examines both research and development challenges in the area of co-operative diversity for enhancing channel capacity in wireless communications networks. In particular, the role played by the distributed coding protocols in achieving diversity gains is investigated in connection with the co-operative communications model built via relay channels. A coding scheme suitable for the nodes working collaboratively in this environment is also presented.

Many applications in wireless networks impose locally distributed traffic on the network. We consider the effect of traffic localization on throughput of large wireless networks in the scaling sense. We show that by careful exploitation of traffic localization, one can enhance the throughput of various schemes in wireless networks. Also, the important case of Small World traffic distribution in wireless networks is addressed. In this type of traffic, in addition to the local traffic, a non-negligible amount of global traffic should be handled by the network. It is shown that a non-negligible amount of network-wide traffic can be tolerated by network without any performance degradation in the scaling sense.

In this paper, NPS (neural-network prediction scheme) is proposed to provide high accurate location prediction of a MH (mobile host) in wireless networks. Currently, multimedia communications is urgently expected in wireless networks, because more and more high-speed applications emerge for wireless networks. One of the most important and complicated issues is quality of service (QoS) in third-generation (3G) wireless networks. In other words, the problem to maintain the playing continuity of multimedia streams during a handoff is hard to solve. Hence, bandwidth reservation scheme is proposed in this paper. In order to avoid too early or over reservation resulting in a waste of resources, we present a method called three-times resource-reservation scheme (TTRR) to let reserved resource become really active upon MH entering into tier-2 [C.H. Choi et al., 2000] area of a cell. NPS and TTRR can efficiently improve the accuracy of MH's trajectory prediction, increase the success probability of resource reservation, and enhance bandwidth utilization.

In multiuser wireless networks, opportunistic scheduling can improve the system throughput and thus reduce the total completion time. In this paper, we explore the possibility of reducing the completion time further by incorporating traffic information into opportunistic scheduling. In particular, we first establish general properties for opportunistic scheduling with file size information. Then, we develop new traffic aided opportunistic scheduling (TAOS) schemes by making use of file size information and channel variation in a unified manner. We also derive lower and upper bounds on the total completion time. Our results show that the proposed TAOS schemes can yield significant reduction in the total completion time

With the rapid development of wireless network technology, energy saving has become a very important topic to build a green network in wireless networks. Due to the time-varying characteristics of the channel, it is possible to obtain a higher utilization for energy by using the channel with good state in wireless communications. From the view of the data transmission energy consumption of the whole wireless network, this paper proposes an expected energy consumption minimization strategy (E2CMS) for data transmission based on the optimal stopping theory. Considering the maximum transmission delay and a given receiving power, E2CMS delays data to transmit until the best expected channel state is detected. In order to solve the problem, firstly, we construct an energy consumption minimization problem with quality of service constraints. Then, we prove that E2CMS is a pure threshold strategy by the optimal stopping theory and obtain the power threshold by solving a fixed-point equation using backward induction. Finally, simulations are performed in a typical small-scale fading channel model. E2CMS is compared with a variety of different transmission scheduling strategies. The results show that E2CMS has lower average energy consumption for per unit data and significantly improves the network performance.

SUMMARYResource reservation or the other prioritization strategies adopted by Call Admission Control (CAC) schemes in wireless networks lead to unfair resource allocation to users belonging to different service classes (SCs) due to high divergence among the respective call blocking probabilities (CBPs). In this paper, we propose dynamic optimization of probabilistic CAC (P‐CAC) schemes to assure CAC fairness among users of different SCs in wireless networks. The approach is based on users utility combined with fairness optimization, aiming at dynamically determining the probability value in the P‐CAC scheme. This optimal probability is adjusted to network ongoing traffic, CBPs of each SC, prioritization levels characterizing the SCs supported, and the users risk aversion, which reflects their behavior toward the perceived QoS. The existence and uniqueness of the optimal probability that leads to absolute fairness among the users of a wireless network are proven. Copyright © 2012 John Wiley & Sons, Ltd.